National Research Council of Canada

Thomas A Tweedle

Oleh Kutowy

Andre Y Tremblay

A method of casting porous membranes of polymeric material is provided wherein the membrane has at least one of the following: a more homogeneous active skin layer for separation purposes with a lower molecular weight cut off, a more homogeneous active skin layer with a sharper molecular weight cut off curve, a relatively thinner active skin layer with a relatively greater flux for a given separation of a substance from a solution thereof, and relatively fewer imperfections through the active skin layer. The method comprises casting a layer of a casting solution on to a support, to provide a cast layer of the casting solution thereon with an exposed skin, then progressively submerging the cast layer in a gelation liquid at a relative velocity of at least 15 cm/second, whereby the exposed skin is gently scrubbed with gelation liquid to continuously remove outwardly diffusing solvent therefrom and dissipate exothermic heat, thus causing gelation of at least a stable, more homogeneous active skin layer, with build-up of a solvent boundary layer between the exposed surface of the layer and the gelation liquid minimized.

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Orleans, Canada

Thomas A Tweedle